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1989 Ford 5.0 cylinder misfire. HELP
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burns201
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Apr 11, 2014, 8:53 PM
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1989 Ford 5.0 cylinder misfire. HELP
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My 1975 Maverick has a 89 5.0. Cylinder 4 is dead (rear cylinder passenger side). Not firing and blowing lots of gas out of the exhaust. It has a street avenger carb, weiand intake, MSD 6al, msd coil, msd wires, msd cap and rotor and stock distributor. It has spark at the cylinder. I even swapped out the MSD box, cap and rotor, plug wires and got new plugs(same problem). Took off carb, cleaned and reinstalled(still same problem). Tried a friends edelbrock carb(same problem). Compression tested all cylinders and all are good. Checked valves and they are opening as they should. Looked in cylinder with camera and it still looks new. Roller rockers rock as they should. I am at a loss. I am thinking either the Distributor (even though it has spark possibly just not firing at the correct time), or could it be a intake manifold or head gasket leak. Any help would be greatly appreciated. I have been trying to figure this out since September. Thanks
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nickwarner
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Apr 12, 2014, 1:10 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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I would wonder about the distributor. With a full MSD set, why are you running an OE distributor? Strange to see it affect just that cylinder but possible.
What test told you that is was indeed cylinder 4. That also is not the rear cylinder. Rear cylinders on a 302 are 7 and 8. Cylinder 4 is in the middle
(This post was edited by nickwarner on Apr 12, 2014, 1:11 AM)
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burns201
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Apr 12, 2014, 6:27 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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I know it is the rear cylinder on passenger side b/c the plug is just wet with gas and the header does not get hot. I have the HO firing order which is 1,2,3,4 on passenger side. The engine is an 1989 5.0 switched to a Holley carb. Is it possible it doesn't have enough spark when the cylinder is under pressure?
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Hammer Time
Ultimate Carjunky
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Apr 12, 2014, 7:01 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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Sure it's possible but you can easily test the quality of the spark with a spark tester.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Apr 12, 2014, 7:33 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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Just curious, but what were your compression numbers?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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burns201
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Apr 12, 2014, 7:52 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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All cylinders read 145-150. The dead cylinder reads 230 but both of my mechanics said that is from the uncombusted gas taking up space in the combustion chamber.
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Discretesignals
Ultimate Carjunky
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Apr 12, 2014, 8:07 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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That isn't right. 230 is way too high. Uncombusted gasses? When your doing a static compression test the gases that are pulled into the cylinder are not combusted anyway because the engine is disabled from running.
You need to have them do a dynamic compression test or running compression test to figure out if that cylinder is breathing or not.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Apr 12, 2014, 8:09 AM)
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burns201
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Apr 12, 2014, 8:16 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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We put a scope in the cylinder and watched the valves open and close. I am leaning towards the spark on that cylinder just not being strong enough.
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kev2
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Apr 12, 2014, 9:02 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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230 psi. Uncombusted gasses?
Remove the valve cover and observe the valve train.
Crank the engine with all plugs out- any evidence of coolant or oil in cylinder?
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burns201
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Apr 12, 2014, 9:09 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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Took valve covers off twice. The rockers rock as they should and the push rods spin at TDC like they should. I double checked it b/c I thought that had to be the problem.
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burns201
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Apr 12, 2014, 9:15 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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No coolant or oil in cylinder, just gas.
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Discretesignals
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Apr 12, 2014, 10:38 AM
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Re: 1989 Ford 5.0 cylinder misfire. HELP
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Like you have stated check your spark output. The spark should be in the 30kV range. You can also take a 12 volt test light grounded to the battery negative to check the spark status.
Remove the spark plug wire from the plug and hold the probe of the test lamp inside the boot, so it is touching the terminal. Start the engine. With the engine running move the probe away from the terminal. The spark should be able to jump at least a 3/4 inch gap to your test light. Test a known good cylinder for comparison.
The spark tester HT provided a picture of works the same way, but if you have a 12 test light laying around, you can use that too.
Don't run the engine with nothing for the spark to jump to or you can damage the coil. Also don't let yourself become ground, because getting zapped kind of hurts.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Apr 12, 2014, 10:39 AM)
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